Various types of hearing devices provide people with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
People with some forms of conductive hearing loss may benefit from hearing devices such as hearing aids or electromechanical hearing devices. A hearing aid, for instance, typically includes at least one small microphone to receive sound, an amplifier to amplify certain portions of the received sound, and a small speaker to transmit the amplified sounds into the recipient's ear. An electromechanical hearing device, on the other hand, typically includes at least one small microphone to receive sound and a mechanism that delivers a mechanical force to a bone (e.g., the recipient's skull, or a middle-ear bone such as the stapes) or to a prosthetic (e.g., a prosthetic stapes implanted in the recipient's middle ear), thereby causing vibrations in cochlear fluid.
Further, people with certain forms of sensorineural hearing loss may benefit from hearing devices such as cochlear implants and/or auditory brainstem implants. Cochlear implants, for example, include at least one microphone to receive sound, a unit to convert the sound to a series of electrical stimulation signals, and an array of electrodes to deliver the stimulation signals to the recipient's cochlea so as to help the recipient perceive sound. Auditory brainstem implants use technology similar to cochlear implants, but instead of applying electrical stimulation to a recipient's cochlea, they apply electrical stimulation directly to a recipient's brain stem, bypassing the cochlea altogether while still helping the recipient perceive sound.
In addition, some people may benefit from hearing devices that combine one or more characteristics of the acoustic hearing aids, vibration-based hearing devices, cochlear implants, and/or auditory brainstem implants to perceive sound.
Hearing devices such as these typically include an external processing unit that typically performs at least some sound-processing functions and an internal stimulation unit that at least delivers a stimulus to a body part in an auditory pathway of the recipient. The auditory pathway includes a cochlea, an auditory nerve, a region of the recipient's brain, or any other body part that contributes to the perception of sound. In the case of a totally-implantable hearing device, the stimulation unit includes both processing and stimulation components, though the external unit may still perform some processing functions when communicatively coupled or connected to the stimulation unit.